Thin film inductive heads are used to read and write data to and from an adjacent disc surface. Typically, the inductive head includes a top and bottom magnetic pole separated by a gap of insulating material, with a conductive coil embedded in the insulating material of the gap distal from the air bearing surface (ABS) of the head. Typically, the bottom pole and insulating gap are not of critical dimension to the width of the recording track, as the track width is defined by the width of the top magnetic pole at the air bearing surface. (Of course, the thickness of the insulating material forming the gap is critical since it defines the bit length of the recorded track.)
The elements of the thin film inductive head are usually formed by a photolithographic process. The photolithographic mask defining the top pole piece includes a trench that extends from the paddle region of the pole (where the coils form a hill in the insulating material) to the ABS. The trench defines the width of the top pole piece at the ABS, and hence the width of the track. As track width dimensions become smaller and the radial track density (number of tracks per inch) increases, the aspect ratio of the trench pattern in the photoresist forming the top pole piece becomes increasingly critical. More particularly, the top pole is created by depositing the magnetic material into the trench in the photolithographic mask formed on the insulating layer. If the trench is not well defined, or if it includes debris, the resulting top pole piece is not well defined at the ABS, leading to adverse operation of the head. Typically, the photolithographic mask is quite thick (about 13 microns) compared to the width of the mask trench at the gap (typically less than about 2 microns).
The photolithographic mask is ordinarily formed by spinning the photolithographic material, such as a photoresist, onto the insulating layer of the head to a thickness of about 13 microns. The coil configuration within the head forms a sloped hill portion to the insulating layer having a raised portion (where the paddle region of the top pole will be placed) and sloping downhill to the gap at the ABS. In forming the mask, the photoresist is spun over the hill, including on the slope, and past the intended ABS to a waste area. The photolithographic material is then patterned to the shape of the desired pole over the insulating material, to define the paddle and gap regions of the pole and a feeder region in the waste area. The photolithographic material is then exposed and thereafter washed out with a solvent. Typically, the solvent is applied to the exposed portions of the photoresist at the paddle region and in the feeder region and allowed to flow from the feeder region, through the trench area and into the paddle region. However, the flow of the solvent through the trench region of the photoresist often creates residue in that trench region, resulting in a poorly defined trench and adversely affecting the deposit of magnetic material within the trench to define the gap at the air bearing surface. As a result, when the head is later diced and milled at the ABS, unwanted residue within the mask inhibits proper formation of the magnetic pole at the gap, resulting in unacceptable performance of the head.
To achieve a well-defined, acceptably clear trench for formation of the gap region of the top pole piece, the solvent must be evenly applied to the photolithographic mask material. This requirement has heretofore been a limiting factor on the width of the trench, and hence the width of the top pole piece at the ABS. For this reason, it is not been practical, prior to the present invention, to achieve gap widths for inductive magnetic heads less than about 1.8 microns. We have discovered, however, that trenches with smaller widths and higher aspect ratios (height to width) can be achieved by applying a laminar flow of the solvent through the trench.